Phase space density limitation in laser cooling without spontaneous emission

We study the possibility to enhance the phase space density of non-interacting particles submitted to a classical laser field without spontaneous emission. We clearly state that, when no spontaneous emission is present, a quantum description of the atomic motion is more reliable than semi-classical description which can lead to large errors especially if no care is taken to smooth structures smaller than the Heisenberg uncertainty principle. Whatever the definition of position - momentum phase space density, its gain is severely bounded especially when started from a thermal sample. More precisely, the maximum phase space density, can only be improved by a factor M for M-level atoms. This bound comes from a transfer between the external and internal degrees of freedom. To circumvent this limit, one can use non-coherent light fields, informational feedback cooling schemes, involve collectives states between fields and atoms, or allow a single spontaneous emission evenComment: 3 figures, 4 page

The costs and benefits of complying with the tax system and their impact on the financial management of the small firm

Empirical research carried out in different countries provides strong evidence that tax compliance costs impact more heavily on small firms. In addition, results showed that the regressivity of tax compliance costs according to size was even more accentuated after taking into consideration the effects of the cash flow and tax deductibility benefits of tax compliance. However, it has been suggested in the literature that business taxpayers could also be deriving managerial benefits as a result of complying with tax. These managerial benefits are expected to come in the form of a better knowledge of financial affairs and the improved decision-making that will be brought about by the more stringent record keeping imposed by tax requirements. The existing evidence indicates that these managerial benefits could be significant, particularly in smaller firms where accounting systems are initially un-developed. The paper argues that in spite of the abundance of descriptive research in the field, the incidence of tax compliance activities on small businesses is still incompletely understood. Very little explanatory research has attempted to study the relationships between potential influencing factors and the magnitude of tax compliance costs. Likewise, the managerial benefits of tax compliance are still largely un-explored. Fresh empirical data and further investigation are necessary in order to identify the conditions in which managerial benefits may be derived and measure their impact on the financial management of the small firm

Reversible Destruction of Dynamical Localization

Dynamical localization is a localization phenomenon taking place, for example, in the quantum periodically-driven kicked rotor. It is due to subtle quantum destructive interferences and is thus of intrinsic quantum origin. It has been shown that deviation from strict periodicity in the driving rapidly destroys dynamical localization. We report experimental results showing that this destruction is partially reversible when the deterministic perturbation that destroyed it is slowly reversed. We also provide an explanation for the partial character of the reversibility.Comment: 4 pages, 2 eps figures (color

Resonantly enhanced tunneling of Bose-Einstein condensates in periodic potentials

We report on measurements of resonantly enhanced tunneling of Bose-Einstein condensates loaded into an optical lattice. By controlling the initial conditions of our system we were able to observe resonant tunneling in the ground and the first two excited states of the lattice wells. We also investigated the effect of the intrinsic nonlinearity of the condensate on the tunneling resonances.Comment: accepted for publication in Phys. Rev. Letter

Dynamical control of matter-wave tunneling in periodic potentials

We report on measurements of dynamical suppression of inter-well tunneling of a Bose-Einstein condensate (BEC) in a strongly driven optical lattice. The strong driving is a sinusoidal shaking of the lattice corresponding to a time-varying linear potential, and the tunneling is measured by letting the BEC freely expand in the lattice. The measured tunneling rate is reduced and, for certain values of the shaking parameter, completely suppressed. Our results are in excellent agreement with theoretical predictions. Furthermore, we have verified that in general the strong shaking does not destroy the phase coherence of the BEC, opening up the possibility of realizing quantum phase transitions by using the shaking strength as the control parameter.Comment: 5 pages, 3 figure

Exploring dynamic localization with a Bose-Einstein condensate

We report on the experimental observation of dynamic localization of a Bose-Einstein condensate in a shaken optical lattice, both for sinusoidal and square-wave forcing. The formulation of this effect in terms of a quasienergy band collapse, backed by the excellent agreement of the observed collapse points with the theoretical predictions, suggests the feasibility of systematic quasienergy band engineering.Comment: 7 pages, 4 figure

Triplet-singlet conversion by broadband optical pumping

We demonstrate the conversion of cold Cs_{2} molecules initially distributed over several vibrational levels of the lowest triplet state a^{3}\Sigma_{u}^{+} into the singlet ground state X^{1}\Sigma_{g}^{+}. This conversion is realized by a broadband laser exciting the molecules to a well-chosen state from which they may decay to the singlet state throug\textcolor{black}{h two sequential single-photon emission steps: Th}e first photon populates levels with mixed triplet-singlet character, making possible a second spontaneous emission down to several vibrational levels of the X^{1}\Sigma_{g}^{+} states. By adding an optical scheme for vibrational cooling, a substantial fraction of molecules are transferred to the ground vibrational level of the singlet state. The efficiency of the conversion process, with and without vibrational cooling, is discussed at the end of the article. The presented conversion is general in scope and could be extended to other molecules.Comment: 5 pages, 4 figure